wireguard: bump to 1.0.20200729

wireguard: bump to 1.0.20200729

* compat: rhel 8.3 beta removed nf_nat_core.h
* compat: ipv6_dst_lookup_flow was ported to rhel 7.9 beta

This compat tag adds support for RHEL 8.3 beta and RHEL 7.9 beta, in addition
to RHEL 8.2 and RHEL 7.8. It also marks the first time that
<https://www.wireguard.com/build-status/> is all green for all RHEL kernels.
After quite a bit of trickery, we've finally got the RHEL kernels building
automatically.

* compat: allow override of depmod basedir

When building in an environment with a different modules install path, it's
not possible to override the depmod basedir flag by setting the DEPMODBASEDIR
environment variable.

* compat: add missing headers for ip_tunnel_parse_protocol

This fixes compilation with some unusual configurations.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>